The present invention relates generally to a method of controlling a plurality of actuators of an aerodynamic vehicle and, more particularly, to a method for controlling a plurality of actuators of an aerodynamic vehicle in order to efficiently cause a desired change in the time rate of change of the system state vector of the erodynamic vehicle.
Flight control of aerodynamic vehicles, such as aircraft, is accomplished via a variety of flight control actuators. These flight control actuators include aerodynamic controls such as the rudder, elevators, ailerons, speed brakes, engine thrust variations, thrust vectoring and the like. By altering the various flight control actuators, the system state vector that defines the current state of the aerodynamic vehicle can be changed. In this regard, the system state vector of an aerodynamic vehicle typically defines a plurality of current vehicle states such as the angle of attack, the angle of side slip, the air speed, the vehicle attitude and the like.
Historically, the flight control actuators were directly linked to various input devices operated by the pilot. For example, flight control actuators have been linked via cabling to the throttle levers and the control column or stick. More recently, the flight control actuators have been driven by a flight control computer which, in turn, receives inputs from the various input devices operated by the pilot. By appropriately adjusting the input devices, a pilot may therefore controllably alter the time rate of change of the current system state vector of the aerodynamic vehicle.
Unfortunately, flight control actuators may occasionally fail, thereby adversely affecting the ability of conventional control systems to maintain the dynamic stability and performance of the aerodynamic vehicle. In order to accommodate failures of one or more of the flight control actuators, actuator failure detection and flight control reconfiguration systems have been developed. These systems typically remove the flight control actuator that has been identified as inoperable from the control system. These systems are therefore designed to detect the failure of one or more flight control actuators and to alter the control logic associated with one or more of the flight control actuators that remain operable in an attempt to produce the desired change in the time rate of change of the current system state vector of an aerodynamic vehicle requested by the pilot. These actuator failure detection and flight control reconfiguration systems are highly complex. As such, the proper operation of these systems is difficult to verify. Moreover, these systems introduce a risk that a flight control actuator that is actually functioning properly may be falsely identified as having failed and thereafter removed from the control system, thereby potentially and unnecessarily rendering the control system less effective.
Additionally, flight control actuators generally have some limitations on their performance. In this regard, the rate of change accommodated by most flight control actuators is generally limited to a range bounded by upper and lower limits. Similarly, the actual position which many flight control actuators may assume is also typically limited to a range bounded by upper and lower limits. Unfortunately, conventional control systems do not accommodate limitations in the range of positions and rate of change of a flight control actuator. As such, conventional control systems may attempt to alter a flight control actuator in a manner that exceeds its limitations. Since the flight control actuator will be unable to make the desired change, the control system may correspondingly fail to produce the desired change in the time rate of change of the system state vector of the aerodynamic vehicle.
As such, it would be desirable to develop an improved method for controlling the actuators of an aerodynamic vehicle. In particular, it would be desirable to develop a method of controlling an aerodynamic vehicle which provides increased flexibility with respect to the removal or inclusion of a flight control actuator that may have failed. In addition, it would be advantageous to provide a method for controlling the actuators of an aerodynamic vehicle in a manner that recognizes and accommodates limitations in the range of positions and rate of change of at least some of the actuators.
An improved method and computer program product are therefore provided for controlling the plurality of actuators of an aerodynamic vehicle in order to efficiently bring about a desired change in the time rate of change of the system state vector of the aerodynamic vehicle. In this regard, the method and computer program product of one aspect of the present invention permits the control of the actuators to be tailored based upon predetermined criteria, such as the relative importance of the respective states of the aerodynamic vehicle and/or the weighting to be given to any outlier measurements. According to another aspect, the method and computer program product control the plurality of actuators while recognizing limitations upon the permissible changes to at least one actuator, such as limitations upon the rate of change or the range of positions of at least one actuator. As such, the method and computer program product of the present invention address the shortcomings of conventional control systems and efficiently command the actuators so as to alter the time rate of change of the system state vector of the aerodynamic vehicle in a desired manner.
The method and computer program product control the actuators of an aerodynamic vehicle by initially determining the differences between anticipated changes in the plurality of states of the aerodynamic vehicle based upon the current condition of each of the actuators and desired changes in the plurality of states of the aerodynamic vehicle. In order to determine the differences between the anticipated and desired changes in the plurality of state rates of the aerodynamic vehicle, the dot product of a vector representing the current commanded state of each actuator and a matrix representing changes in the plurality of states of the aerodynamic vehicle in response to changes in the actuators is initially determined. In this regard, the matrix includes a plurality of terms, each of which represents the anticipated change in a respective state rate of the aerodynamic vehicle in response to the change of a respective actuator. In order to determine the difference between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle, the vector difference between the dot product and a vector representing the desired change in the plurality of states of the aerodynamic vehicle is then obtained.
According to one aspect of the present invention, the differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle are then weighted based upon a predetermined criteria. In this regard, the differences may be weighted based upon the relative importance of the respective states of the aerodynamic vehicle, thereby permitting those states which are believed to be of greater importance to be assigned a correspondingly greater weight. As a result of this greater weight, the method and computer program product of this aspect of the present invention will control the actuators so as to more quickly alter these states than other states having lower weights assigned thereto. In addition or in the alternate, the differences may be nonlinearly weighted by a predefined penalty based upon the emphasis to be placed upon outliers, i.e., relatively large differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle.
Based upon the weighted differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle, the method and computer program product may determine a second dot product of the weighted vector difference and a transpose of the matrix representing changes in the state rates of the aerodynamic vehicle in response to changes in the plurality of actuators. The second dot product therefore represents the changes in the actuators required to affect the desired changes in the plurality of states of the aerodynamic vehicle, given the anticipated changes in the plurality of states. As such, the weightings assigned to the respective states of the aerodynamic vehicle will correspondingly effect changes in the desired state of the actuators. The second dot product may also be weighted by a gain matrix, one term of which is associated with each actuator in order to appropriately weight the relative contributions of the actuators.
According to another advantageous aspect of the present invention, the method and computer program product may also limit the permissible changes of at least one of the actuators. In this regard, the permissible rate of change of one or more of the actuators may be limited. Similarly, the position of one or more of the actuators may also be limited to within a predefined range. As such, the method and computer program product of the present invention effectively recognize and accommodate limitations of the actuators, thereby preventing any attempts to drive the actuators beyond their predefined limitations.
The method and computer program product then issue control signals to the plurality of actuators so as to implement at least a portion of the desired change in the time rate of change of the system state vector of the aerodynamic vehicle. In those aspects of the present invention in which the differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle are weighted, the control signals are at least partially based upon the weighted differences. More particularly, in those embodiments in which the second dot product of the weighted vector difference and the transpose of the matrix representing changes in the system state vector of the aerodynamic vehicle in response to the changes in the plurality of actuators is determined, the control signals are at least partially based upon the second dot product. Moreover, the control signals may be more directly weighted by the gain matrix. Additionally, in those aspects of the present invention in which the permissible changes of at least one of the actuators is limited, the control signals issued to the actuators are subject to the limitations in the permissible changes of one or more of the actuators. Thus, at least a portion of the desired change in the plurality of states of the aerodynamic vehicle may be implemented without exceeding the permissible changes of the actuators.
Thus, the method and computer program product of the present invention provide an improved technique for efficiently controlling the actuators of an aerodynamic vehicle in order to effect the desired change in the time rate of change of the system state vector of the aerodynamic vehicle. According to one aspect of the present invention, the control of the actuators may be influenced by weighting based upon a predetermined criteria, thereby permitting the control system to be more individually tailored. Based upon the weighting, the method and computer program product also bring about the desired change in the time rate of change of the system state vector of the aerodynamic vehicle in the most efficient manner by minimizing the cost as defined at least partially by the weighting. According to another aspect of the present invention, the permissible changes of one or more of the actuators may be limited such that the desired change in the time rate of change of the system state vector of the aerodynamic vehicle may be affected without attempting to exceed the permissible changes of at one or more of the actuators.